1. Field of the Invention
The present invention relates to a keyswitch assembly and, more particularly, to a keyswitch assembly consisting of a relatively small number of parts, having a simple construction, capable of being manufactured at a relatively low manufacturing cost and suitable for use on a thin keyboard for a portable word processor, a portable personal computer or the like.
2. Description of Related Art
A known keyswitch assembly for use on such a keyboard has a key provided with a stem, a base plate provided with a key support having a hole receiving the stem of the key to guide the key for vertical movement, and a switching member, such as a membrane switch, disposed under the stem. When the key is depressed, the lower end of the stem of the key presses the switching member for switching action.
A keyswitch assembly provided with a large key, such as a space key and a return key, is provided with a mechanism for maintaining the key supported on a base plate in a level position when the key is depressed. Such keyswitch assemblies are disclosed in U.S. Pat. Nos. 4,580,022, 4,902,862 and 4,433,225.
In a keyswitch assembly disclosed in the '022 patent, a key member is supported on support levers connected with pins in a scissors-like form, and switching members are disposed apart from the central portion of the key member. Pins attached to the opposite ends of the support levers slide horizontally along the inner surface of the key member and the upper surface of a base plate when the key member is depressed. Stems formed in the key member and guided by a guide member slide vertically to compress the switching members when the key member is depressed.
A keyswitch assembly disclosed in the '862 patent is the same in basic construction as the keyswitch assembly disclosed in the '022 patent and is characterized in that the key member can be easily connected to and removed from the support levers which are coupled to a base plate.
In the '225 patent, a keyswitch assembly including an L-shaped keytop is disclosed. The keyswitch assembly comprises a pair of lever arms joined at intermediate portions thereof by a pivot to form a scissors-like linkage having first, second, third, and fourth ends. The first and second ends of the scissors-like linkage are pivotally slidable within the cantilevered portion of the keytop. However, a keyswitch portion is separately disposed from the scissors-like linkage. So, there is a problem that the keyswitch is not perfectly operated. Furthermore, a plunger and base plate are needed, so the assembly requires many parts, and the structure is complex.
Recent progressive reduction in size and thickness of word processors and personal computers requires reduction in size and thickness of keyboards to be incorporated into word processors and personal computers. On the other hand, the keys of keyboards must be adequately supported to facilitate keystroke operation and to secure a reliable keystroke. The prior art keyswitch assemblies, therefore, utilize base plates to secure the key support member thereto.
The keyswitch assemblies disclosed in the foregoing references are not intended to enable the reduction of the thickness of the keyboard. Since all of the above references require a base plate, none of these references are able to reduce the thickness and weight of the keyboard satisfactorily.
Further, the manufacturing cost of a base plate is relatively high and adds to the total cost of the keyboard.